A comprehensive study of Al-Cu-Mg system reinforced with nano-ZrO2 particles synthesized by powder metallurgy technique

More focus has recently been placed on enhancing the strength, elastic modulus, coefficient of thermal expansion (CTE), wear and corrosion resistance, and other qualities of aluminum (Al) alloys by varying the quantity of ceramics added for a range of industrial uses. In this regard, Al-4.2-Cu-1.6Mg matrix nanocomposites reinforced with nano-ZrO2 particles have been created using the powder metallurgy approach. The microstructure and particle size distributions of the produced powders were analyzed using a diffraction particle size analyzer, XRD, TEM, and SEM. To achieve good sinterability, the powders were compacted and sintered in argon. The sintered nanocomposites' mechanical, elastic, and physicochemical characteristics were measured. Additionally, the behavior of corrosion, wear, and thermal expansion were examined. The results showed a decrease in the particle sizes of the Al-Cu-Mg alloy by adding ZrO2 nanoparticles up to 45.8 nm for the composite containing 16 wt.% ZrO2. By increasing the sintering temperature to 570 °C, the densification of nanocomposites was enhanced. Also, the coefficient of thermal expansion and wear rate remarkably decreased by about 28 and 37.5% by adding 16 wt.% ZrO2. Moreover, microhardness yield, strength, and Young’s modulus were enhanced to 161, 145, and 64%, respectively, after adding 16 wt.% ZrO2. In addition, increasing the exposure time was responsible for decreasing the corrosion rate for the same sample.

respectively, by adding 8 vol.% of SiC particles.ZrO 2 nanoparticles were mechanically alloyed with Al2024 alloy powder by Youness et al. 9 to create nanocomposite powders with varying ZrO 2 concentrations.Following that, they underwent argon atmosphere pressing and sintering to get bulk nanocomposite samples.By adding more ZrO 2 , the nanocomposites' microhardness and compressive strength were greatly enhanced.Muralidharah et al. 10 studied the effect of different ZrO 2 weight percentages up to 12 wt.% on the mechanical properties of the Al 6061 alloy using stir casting.It was nanocomposites that observed an improvement in mechanical properties by adding ZrO 2 particles.AbuShanab et al. 11 extensively studied the effect of graphene weight percent on Al2024 alloy matrix nancomposites using powder metallurgy methods.Their results showed graphene's effect on microstructure, mechanical and thermal expansion, corrosion behavior, and these metal matrixes' electrical properties.Importantly, the addition of ceramics like SiC 12 , Al 2 O 3 13 , ZrO 2 4,9,10,14 , TiC 15 , and graphene 6 is considered the optimal solution to overcome this serious obstacle.In this sense, finely stabilized ZrO 2 is a good choice for this required task due to its superior mechanical properties, high melting temperature, better corrosion resistance, and perfect corrosion resistance compared to Al and its alloys' thermal and chemical stability 4,16 .Under the effect of its particle size, the interaction of particles with dislocations easily occurs, which consequently has a great significance for the enhancement of densification of the sintered samples and, consequently, the improvement of wear, corrosion resistance, and mechanical properties 17 .
It is important to emphasize that there are many effective methods to produce Al and its alloy matrix nanocomposites, such as fraction stir 18 , squeeze casting 19 , stir casting 20 , and powder metallurgy (PM) 21,22 .The latter is a modern and cost-effective tool for good dispersion of reinforcement in the matrix, giving a uniform distribution of particles in the microstructure 23,24 .Due to these benefits, the mechanical alloying (MA) technique has been used as one of the most effective PM methods to prepare desired nanocomposites.During the MA process, powders undergo a fracturing and welding process for powder particles that is highly dependent on key parameters such as milling time, speed, mill type, ball-to-powder (BPR) ratio, and vial/ball material, which thus control the size and shape of the reinforcement material produced 25 .
Based on the abovementioned advantages of PM, this process can fabricate various MMCs with desirable properties 26 .In previous research, the effect of different ceramics, including ZrO 2 , on some properties of Al-Cu-Mg alloys prepared by different methods such as stir castand others, was studied, and this is the reason why the use of aluminum alloys is restricted in many industries.Based on these facts, the goal is an extensive study to improve the mechanical and elastic properties, the coefficient of thermal expansion, and its resistance to abrasion and corrosion by adding different percentages of nano-ZrO 2 particles, up to 16% by weight, prepared by powder metallurgy.

Materials and experimental setup
In this work, we selected an Al-4.2Cu-1.6MgAl alloy as a matrix, and nano-ZrO 2 (< 50 nm) particles used as reinforced with various weight percentages up to 16 wt.%.The mechanical alloying method used to prepare the Al-4.2Cu-1.6Mgalloy, the following commercial materials have been used: Al (99.9 wt.%), Cu (99.9 wt.%), and Mg (99.95 wt.%).Al alloy components have been blended with a planetary ball mill for 20 h with rotation speed = 120 rpm.In order to obtain nanocomposites, the nano-ZrO 2 was added with different weight percentages to the Al-10Si-0.6Mgalloy shown in Table 1.Subsequently, these mixtures were subjected to the a milling process for 20 h with rotation speed = 500 rpm having in mind that the milling process was done in a cycle of 2 h and paused for 2 h.
To investigate the morphology of the mechanically alloyed powders, they were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM, type JEOL JEM-1230) and particle size was measured using a diffraction particle size analyzer to get the average distribution pattern for each powder.According to in our work 6 , the crystallite size of milled powders was calculated depending on the broadening of the diffraction peaks using the Scherrer equation.Then, the milled powders were pressed and sintered at 470 and 570 °C in an argon atmosphere for 1 h.Notably, the rule of mixture was carried out to calculate the theoretical densities of samples taking into account the density of the Al-Cu-Mg alloy = 2.7 g/cm 3 and the density of ZrO 2 = 5.68 g/cm 3 .On the other hand, Archimedes method was carried out to measure both bulk density and apparent porosity.The sintered samples' microstructure was investigated by scanning electron microscopy (SEM; Philips XL30).Moreover, using (Netzsch DIL402 PC; Germany), thermal expansion of specimens was measured in the range from 30 to 400 °C.Vickers microhardness (HV) was measured with a Shimadzu-HMV (Japan) according to ASTM: B933-09 as described in Ref. 27 .Furthermore, the compressive tests of the sintered nanocomposites were performed according to ASTM E9-19 standard.The ultimate strength, yield strength, and elongation were calculated from the stress-strain curve; hence the ultimate strength and elongation are the maximum values of stress and strain on stress-strain curve, respectively.On the other hand, yield strength was calculated using the 0.2% offset principle.Using the pulse-echo technique system, the longitudinal and shear velocities of the ultrasonic wave were obtained at room temperature to obtain Elastic moduli as indicated from Ref. [28][29][30] .The wear test was carried out using a pin-on-disk tester machine; the specimens were weighed and measured by a digital balance of accuracy of 0.0001 g.All samples were prepared with the same dimensions and polished well using grinding papers with different grades (600 to 4000).The test was carried out using four different loads.The wear rate due to the weight loss was calculated from the following equations (Eqs.8 and 9) 31 : The sintered samples' corrosion rate was determined using static immersion weight loss method at room temperature where each sample was weighed before its immersion in 1 M HCL solution and later taken out after 24, 48, 72, 96, 120, 144, and 168 h.After drying thoroughly, the specimens were weighted again.The weight loss was measured and converted into corrosion rate expressed in mm penetration per year (mm/year).The standard deviation of all measured propertes was calculated for 5 samples.

Milled powders
Figure 1 shows the XRD patterns of AZ0, AZ2, AZ4, AZ8 and AZ16 nanocomposites powder after 20 h of milling.The XRD pattern of sample AZ0 (matrix) clearly shows that, in accordance with the card numbers (JCPDS 01-089-4037, 96-901-2197 and 65-2501), the powder's primary phases are Al, Al 2 Cu and MgCuAl 2 , respectively.Cu's solid solubility in the solid Al solution phase caused the Al 2 Cu (precipitation) phase to form, confirming that the alloying process had been effectively completed in accordance with the phase diagram.On the other hand, ZrO 2 peaks appear as a result of its addition in different percentages according to card numbers (JCPDS 86-1450).It is possible to conclude that when ZrO 2 weight percent gradually rises, their broadness increases and their intensities noticeably decrease, which leads to a decrease in the size of the crystals, as shown in Fig. 2. The mean crystal sizes value of the AZ0, AZ2, AZ4, AZ8, and AZ16 specimes were 33.25, 31.34,29.42, 24.98, and 19.52 nm, respectively.
TEM micrographs of as-received ZrO 2 nanoparticles along with those of the Al alloy containing 0, 8, and 16 wt.%ZrO 2 after milling are illustrated in Fig. 3a-d.As can be seen from Fig. 3a, ZrO 2 particles are a little agglomerated, located in the nano-scale range, and their sizes do not exceed 50 nm.The most plausible explanation for these data is that, although the ZrO 2 particles are fragmented during mechanical milling, the Al alloy matrix particles undergo deformation (flatting).ZrO 2 particles sandwich one or more matrix particles at the point of ball contact as the ductile Al alloy matrix particles begin to weld.Real nanocomposite powders are created as a result of ZrO 2 particles residing at the interfacial boundaries of the welded matrix particles 6 .It is noteworthy to observe that the local plastic deformation around the ZrO 2 particles has increased, contributing to the particle size reductions.Additionally, ZrO 2 particles can result in increased energy transmission to the Al alloy matrix by acting as milling balls.On the other hand, with increasing ZrO 2 contents, a fracture-cold welding mechanism quickly occurs 8 .Figure 4 shows the particle size distribution of the all milled powders.As the ZrO 2 weight percent increased, the particle size decreased and the distribution shifted to smaller sizes.The mean particle sizes value of the AZ0, AZ2, AZ4, AZ8, and AZ16 specimes were 97.7, 89.

Physical properties
After the mechanical alloying process, the compaction of the milled nanocomposite powders is often an important step in obtaining bulk materials.Consequently, this stage regulates the final sintered nanocomposites' porosity and form 32 .Figure 5 shows the bar graph that corresponds to the ZrO 2 weight percentages and describes the relative density and apparent porosity of the sintered samples during 1 h at 470 and 570 °C.Furthermore, the standard deviation of the measured relative density and apparent porosity are listed in   has a melting temperature that is around 2715 °C, which is substantially higher than that of the Al matrix.As a result, higher ZrO 2 levels impede the sintering process and function as a barrier against diffusion steps during this process 33 .Conversely, raising the sintering temperature from 470 to 570 °C can effectively improve relative density because it causes more necks to develop between particles and increases the amount of bonding between them 34 .Furthermore, faster solid-state diffusion and improved densification behavior are the results of higher sintering temperatures 35 .By increasing the ZrO 2 contents from 0 to 16 weight percent, the relative density of samples drops from 97.56 to 92.11% when the sintering temperature is equal to 570 °C.Notably, porosity shows the reverse pattern, increasing as ZrO 2 particle concentration in the specimens under study increases.Nevertheless, greater densification behavior that is, almost attaining full density is produced by raising the sintering temperature to 570 °C, which promotes the diffusion process throughout the heating phase.During the sintering of the nanocomposites samples, the contact border between the particles appears to be expanding, signifying the attainment of strong nano-ZrO 2 -matrix interfacial bonding and the absence of pores in the ZrO 2 particle area.

Thermal expansion behavior
Figure 9 depicts the relative thermal expansion (Δl/l) behavior of the sintered Al alloys and nanocomposite samples in the temperature range of 30-400 °C.In the specified temperature range, the un-reinforced Al alloy matrix has a higher Δl/l range from 0.679 × 10 -3 to 9.97 × 10 -3 compared with 0.495 × 10 -3 to 6.45 × 10 -3 for the composite containing 16 wt.% of ZrO 2 particles (AZ16) The variations in CTE of the sintered samples, as determined by the slope of the thermal expansion curve (Fig. 9), are shown in Fig. 10.It is evident that lower CTE values are caused by higher ZrO 2 concentrations.On the other hand, CTE values rise as the sintering temperature rises.
As anticipated, the CTE of the nanocomposite samples is greatly decreased when ZrO 2 particles are added to the Al alloy matrix.This conclusion is supported by the fact that ZrO 2 's CTE is lower than the Al alloy matrix's, thereby limiting Al's thermal expansion and improving the Al alloy matrix's dimensional stability 36 .However, because the CTE values of the ZrO 2 particles and the Al alloy matrix do not match, the addition of ceramic reinforcements (ZrO 2 particles) to the metal matrix (Al alloy) results in residual stresses in the matrix.The Al alloy matrix experiences plastic deformation as a result of thermal stresses, and this process is crucial for enhancing the strength of nanocomposites 37 .www.nature.com/scientificreports/

Elastic and mechanical properties
As seen in Fig. 11, samples sintered at 570 °C were subjected to a non-destructive test (NDT) ultrasonic technique to evaluate the longitudinal (V L ) and shear ultrasonic velocities (V S ).It's interesting to note that rising ZrO 2 levels cause ultrasonic velocities to rise.The findings show that the samples' V L and V S values range from 5886.4 to 7510.2 and 3205.6 4027.2 ms -1 , respectively, with an increase in ZrO 2 concentrations from 0 to 16 wt%.Figure 12 displays the elastic moduli of the studied nanocomposites.Moreover, the standard deviation of the measured ultrasonic velocities, and elastic modili are listed in Table 3.The figure makes it evident that the elastic moduli family has the same pattern for ultrasonic velocities.For instance, the elastic modulus and Poisson's ratio in the AZ0 sample (i.e. the free content of ZrO 2 particles) are 0.2895 and 89.6 GPa, respectively.Remarkably, they rise to 150.5 GPa and 0.2982, respectively, after 16 weight percent ZrO 2 refinement (AZ16).Due to the addition of extremely hard nano-ZrO 2 particles as reinforcement, ultrasonic velocities and elastic moduli significantly improved, entirely agreeing with the exact results of microhardness and compressive strength.Figure 13 displays the average microhardness values, or HV, of the Al alloy and Al alloy-ZrO 2 nanocomposite samples that were sintered at 570 °C and the standard deviation listed in Table 3.The results show that there are noticeable increases in microhardness values when the amount of various ZrO 2 particles in the Al alloy matrix rises.The addition of sixteen weight percent ZrO 2 causes the microhardness of the Al alloy matrix to increase from 431.12 to 1124.5 MPa.The microhardness of nanocomposites samples can be explained by a number of factors, such as the presence of hard ceramic particles, the homogeneous distribution of reinforcement within the matrix, and the reduction of Al alloy matrix grain sizes with increasing ZrO 2 content 39 .
The samples' compressive stress-strain curves are displayed in Fig. 14.It can be shown that Al alloy (AZ0) has a higher elongation and a lower yield end compressive strength than the other samples (AZ2, AZ4, AZ8, and AZ16) at the same sintering temperature.The values of ultimate compression strength (σ ucs ), yield strength (σ y ), and elongation (ε) were derived from the graphs produced from the compression tests of the AZ0, AZ2, AZ4, AZ8, and AZ16 nanocomposites samples.Moreover, the standard deviation of the measured σ ucs , σ y , and ε are listed in Table 3.These values are listed in Table 4.The findings indicate that when ZrO 2 concentrations grow, elongation decreases, and both σ ucs and σ y of all the nanocomposites samples gradually increase.These findings are consistent with the trend in their microhardness results, as depicted in Fig. 13.For AZ0, the values of σ ucs , σ y , and ε are 263.82MPa, 37.57 MPa, and 19.8%, respectively, whereas for AZ16, they were 383.46 MPa, 92.25 MPa, and 12.9%, respectively.
Increases in ultimate and yield strength are often caused by a variety of causes, whereas the following parameters have an impact on the elongation of the Al alloy matrix reinforced with varying ZrO 2 contents: The significant discrepancy in the CTE of the ZrO 2 particles and the Al alloy matrix is linked to thermal mismatch strengthening, which in turn leads to the creation of thermally induced residual stresses 38,39 .The thermal stresses produced in the Al alloy matrix, even at low temperatures, greatly increase the dislocation density close to the interface, strengthening the nanocomposite in the process.
(ii) Orowan strengthening The Orowan strengthening effect, which is caused by the uniform dispersion of the hard ZrO 2 phase into the Al alloy matrix and serves as a barrier to dislocation movement, is essential in improving the mechanical properties of Al matrix nanocomposites.As a result, ZrO 2 particles develop dislocation loops around them, increasing the tension needed to undergo further deformation.
(iii) Load transfer from the Al alloy to the ZrO 2 nanoparticles   In compressive testing, the load transfer, or σ load , between the hard ZrO 2 particles and the Al alloy is determined by Eq. (3) 40 , particularly if there is a sufficient link between the reinforcement of ZrO 2 particles and the Al alloy matrix.
where σ Ym is the yield strength of the matrix.
It can be inferred that adding different ZrO 2 amounts lowers the samples' work hardening capacity (H c ). Equation ( 4) can be utilized to determine the H c of nanocomposites samples by utilizing the values of σ ucs and σ y .
The value of H c for nanocomposites is represented in Table 4 and standard deviation is listed in Table 3 It is interesting to observe that the H c of pressed nanocomposites decreases with an increase in the ZrO 2 nanoparticle   content.The nanocomposites' H c depends on their yield strength, which is further correlated to grain sizes based on the Hall-Petch Eqn.If the grain sizes decrease, the difference in the flow resistance between the grain boundaries is also reduced, leading to an increase in the yield strength leading to decreased work hardening 41 .

Wear analysis
Figure 15 shows the variations in weight loss and wear rate of AZ0, AZ2, AZ4, AZ8, and AZ16 samples with different applied loads.Moreover, the standard deviation of the measured wear rate are listed in Table 5.The findings show that the ,wear resistance of nanocomposite samples tends to rise with increasing ZrO 2 concentrations, while it decreases with increasing load.When applied stresses of 10, 20, and 40 N are used on an unreinforced sample (AZ0), the weight loss is 0.016, 0.0137, and 0.0125 g, respectively.The weight loss is 0.01 g, 0.0083 g, and   www.nature.com/scientificreports/0.0078 g for the sample with 16 weight percent ZrO 2 (AZ16) at the same applied loads.In addition, the wear rates of the nanocomposites samples AZ0, AZ2, AZ4, AZ8, and AZ16 are, respectively, 0.027, 0.025, 0.023, 0.02, and 0.017 mg/s when the applied stress is equivalent to 40 N. Wear resistance is shown to be significantly increased in the produced composites, which is unquestionably a benefit of the incorporation of ceramic particles (ZrO 2 ) 42 .
It is crucial to emphasize that adding ZrO 2 particles to the Al alloy increases the nanocomposites' microhardness and strength, as was previously discussed.As a result, the wear rate decreases following Archad Eq. ( 5) 9 , which helps to explain the enhancement of wear resistance in nanocomposites.
W is wear rate, K is a wear coefficient (constant value), P is the load, and H is the specimen's Vickers hardness.Furthermore, the increase in microhardness is consistent with a decrease in the real area of contact.It is well accepted that the real area of contact can be expressed in terms of the ratio of the normal load to the hardness of the pin material, and accordingly, the decreased real area of contact leads to considerable decreases in wear rate 43 .On the other hand, increases in weight loss and wear rate with increases in the applied load and the surface temperature encourage surface softening, causing more surface and subsurface damage and resulting in decreased wear resistance 44 .

Corrosion analysis
The corrosion behavior of Al or nanocomposites specimens in an acidic medium was assessed using the weightloss method.The corrosion behavior of the nanocomposites under study is often influenced by a wide range of parameters, including weight percentages of ZrO 2 reinforcement, compaction, density, and sintering.This means that after being submerged in 0.1N HCl at room temperature (30 °C), the weight loss and corrosion rate of the AZ0, AZ2, AZ4, AZ8, and AZ16 sintered samples were measured and shown in Fig. 16.Furthermore, the standard deviation of the measured corrosion rate are listed in Table 6.It is noteworthy to note that as exposure time increases, Al alloy matrix nanocomposites lose weight more quickly, which lowers the rate of corrosion.The sample loses weight as exposure time increases because the rate of corrosion reduces with longer contact with an acidic liquid 44 .When the AZ0 sample is immersed for 24, 96, and 168 h, its weight loss is 18.04, 32.52, and 41.65 mg, respectively.When the AZ16 sample, which contains 16 percent ZrO 2 , is immersed for the same amount of time, its weight loss is 6.43, 9.06, and 11.52 mg, respectively.It was also discovered that as ZrO 2 levels increase, weight loss and corrosion rates decrease.Since the ceramic reinforcement particles often don't exhibit any discernible corrosive activity, the presence of ZrO 2 -particles on the surface of nanocomposites samples will keep the surface layer safe in acidic environments [45][46][47] .The corrosion rate of the AZ0 sample is higher than that

Conclusions
In the current study, Al-Cu-Mg alloy-ZrO 2 nanocomposites were prepared using powder metallurgy; the following conclusions were drawn: • Observations were made that the nanocomposites prepared by the powder metallurgy process had a good distribution of nano-ZrO 2 particles in a matrix with noticeable agglomerations.• The particle size reduced with increasing the ZrO 2 particles until they reached 45.8 nm for the sample con- taining 16 wt.%ZrO 2 .• The relative density of the samples decreased with increasing ZrO 2 weight percent, while the apparent porosity increased.• The measurement of thermal expansion reflected that the CTE of the Al alloy was decreased by about 28.2% with the addition of 16 wt.%ZrO 2 particles, indicating the high dimensional stability of nanocomposite samples.• Elastic moduli increased when ZrO 2 quantities increased because the sintered samples' ultrasonic veloci- ties increased as well.Adding 16 weight percent of ZrO 2 improved the bulk and elastic moduli to 70 and 68 percent, respectively.• As the weight percentages of ZrO 2 were increased, the microhardness, ultimate, and yield strength were improved, but the elongation and work hardening were decreased.The AZ16 sample exhibited maximum values for microhardness and ultimate strength, which were found to be approximately 1.8 and 2.1 times greater, respectively, compared to the AZ0 sample.• Specimen wear rates rose with increased load but decreased with increasing ZrO 2 .By adding 12 weight per- cent ZrO 2 particles, the wear rate of the Al alloy was reduced by about 25% compared to the Al alloy matrix.• It has been discovered that raising the weight percentages and exposure times of ZrO 2 particles helps to decrease the rate of corrosion of nanocomposites.

2 )
Figure1shows the XRD patterns of AZ0, AZ2, AZ4, AZ8 and AZ16 nanocomposites powder after 20 h of milling.The XRD pattern of sample AZ0 (matrix) clearly shows that, in accordance with the card numbers (JCPDS 01-089-4037, 96-901-2197 and 65-2501), the powder's primary phases are Al, Al 2 Cu and MgCuAl 2 , respectively.Cu's solid solubility in the solid Al solution phase caused the Al 2 Cu (precipitation) phase to form, confirming that the alloying process had been effectively completed in accordance with the phase diagram.On the other hand, ZrO 2 peaks appear as a result of its addition in different percentages according to card numbers (JCPDS 86-1450).It is possible to conclude that when ZrO 2 weight percent gradually rises, their broadness increases and their intensities noticeably decrease, which leads to a decrease in the size of the crystals, as shown in Fig.2.The mean crystal sizes value of the AZ0, AZ2, AZ4, AZ8, and AZ16 specimes were 33.25, 31.34,29.42, 24.98, and 19.52 nm, respectively.TEM micrographs of as-received ZrO 2 nanoparticles along with those of the Al alloy containing 0, 8, and 16 wt.%ZrO 2 after milling are illustrated in Fig.3a-d.As can be seen from Fig.3a, ZrO 2 particles are a little agglomerated, located in the nano-scale range, and their sizes do not exceed 50 nm.The most plausible explanation for these data is that, although the ZrO 2 particles are fragmented during mechanical milling, the Al alloy matrix particles undergo deformation (flatting).ZrO 2 particles sandwich one or more matrix particles at the point of ball contact as the ductile Al alloy matrix particles begin to weld.Real nanocomposite powders are created as a result of ZrO 2 particles residing at the interfacial boundaries of the welded matrix particles6 .It is noteworthy to observe that the local plastic deformation around the ZrO 2 particles has increased, contributing to the particle size reductions.Additionally, ZrO 2 particles can result in increased energy transmission to the Al alloy matrix by acting as milling balls.On the other hand, with increasing ZrO 2 contents, a fracture-cold welding mechanism quickly occurs8 .Figure4shows the particle size distribution of the all milled powders.As the ZrO 2 weight percent increased, the particle size decreased and the distribution shifted to smaller sizes.The mean particle sizes value of the AZ0, AZ2, AZ4, AZ8, and AZ16 specimes were 97.7, 89.3, 79.4,62.1, and 45.8 nm, respectively.

Figure 2 .
Figure 2. Effect of adding ZrO 2 particle on the crystal size of milled powders.

Figure 4 .
Figure 4. Particle size distribution of the milled powders in various weight percent of ZrO 2 particle.

Figure 5 .
Figure 5. (a) Relative density and (b) apparent porosity of the sintered samples.

Figure 10 .
Figure 10.The changes in CTE values versus ZrO 2 contents of the sintered nanocomposites.

Figure 11 .
Figure 11.Ultrasonic velocities of nanocomposites samples sintered at 570 °C in relation to varying ZrO 2 weight percent.

Figure 12 .
Figure 12.The group of elastic moduli of nanocomposites samples sintered at 570 °C in relation to varying ZrO 2 weight percent.

Figure 15 .
Figure 15.(a) Weight loss and (b) wear rate of sintered samples for different applied loads.

Figure 16 .
Figure 16.(a) Weight loss and (b) corrosion rate of sintered samples for different applied loads.

Table 1 .
The composition of the prepared samples.

Table 2
3 The theoretical densities of AZ0, AZ2, AZ4, AZ8, and AZ16 samples = 2.65, 2.68, 2.71, 2.77, and 2.90 g/cm3, respectively.The relative density values of AZ0 and AZ16 after sintering at 460 °C are 93.22 and 85.96%, respectively.Conversely, the apparent porosity values are 6.88 and 11.01%, respectively, for the same samples sintered at 460 °C.This can be the result of the higher hardness of the ZrO 2 ceramic particles in the Al alloy matrix, which reduces the pressing capacity of the sintered samples as ZrO 2 weight percentages rise.Additionally, ZrO 2 reinforcement

Table 2 .
The standard deviation of relative density and apparent porosity for all samples tested.Microstructure SEM micrographs of the compacted AZ0, AZ4, and AZ16 nanocomposites powders, after 20 h of milling and compressing at 50 MPa, are shown in Fig.6a-c.Careful analyses of SEM micrographs reveal that the distribution of nano-ZrO 2 particles in Al alloy matrix with good densification has a strong role in the mechanical and electrical properties of the final nanocomposites.Figures7 and 8illustrated the SEM images of nanocomposites with different nano-ZrO 2 contents and sintered at 470 and 570 °C along with their corresponding EDS patterns.Generally, at the lower sintering temperature, i.e. 470 °C, nano-ZrO 2 particles are found at the Al alloy matrix's grain borders, considering the sample has the lowest ZrO 2 content exhibits homogenous distribution for ZrO 2 particles noting that this good distribution decreases with increased ZrO 2 contents.Accordingly, the distribution of ZrO 2 particles in both AZ4 nanocomposites specimens is homogenous, while that of AZ16 samples decreases.

Table 3 .
The standard deviation of all mechanical properties for all samples tested.

Table 5 .
The standard deviation of wear rate for all samples tested.This result can be attributed to the high corrosion resistance of ZrO 2 , a ceramic material that resists corrosion well enough to be inert and unaffected by the acidic medium during corrosion tests.After being submerged for 168 h, the corrosion rates of the AZ0, AZ2, AZ4, AZ8, and AZ16 samples are 1.63, 1.46, 1.36, 0.86, and 0.44 mmpy, in that order.

Table 6 .
The standard deviation of corrosion rate for all samples tested.